Seismic surveys are conducted on land and over water to obtain images of subsurface formations to determine the location and extent of hydrocarbons, such as oil and gas. Seismic surveys are typically conducted over land by deploying a large array of seismic sensors over a surface portion of the earth. Typically, such arrays cover several square kilometers, for example 75-100 square kilometers, utilizing a few thousand, for example 2000 to 5000, seismic receivers or sensors. An energy source (typically a buried explosive source or a mobile vibratory source) is activated within the array to generate an acoustic energy (a shock wave) that propagates through the subsurface structures of the earth. A portion of the acoustic wave is reflected back to the surface from underground discontinuities, such as at where the formation rock structure changes and at oil and gas reservoir interfaces. These reflections are sensed by the sensors in the sensor array and processed and recorded by data acquisition units placed proximate the sensors. The data from the recorders is typically collected and sent to a central station for further processing. Such sensing, processing and recording are typically referred to as seismic data acquisition. Seismic data acquisition also is performed in a passive mode, i.e., recording of seismic signals received from the earth subsurface structures without the use of an active acoustic energy source.
A three-dimensional map, or seismic image, of the subsurface structures is generated from the sensor data received by moving the energy source to different locations in the array. This map is then used to make decisions about drilling locations, reservoir size, pay zone depth, etc. The quality and resolution of the seismic image depends upon the density of sensors in the array. Typically greater sensor density, i.e., greater number of sensors in the array, provides sharper and clearer images. Geophones or multi-component (three-axis) accelerometers are generally used as seismic sensors. Multi-component recording, however, provides higher sensor density than single component sensors and also higher amounts of data that is processed and recorded by the data acquisition units in the field.
In one type of seismic surveying, sensor arrays typically include sensors connected in a matrix using point-to-point cable connections for all of the sensors. Output signals from the sensors are usually digitized and relayed down the cable lines to a high-speed backbone field processing devices or field boxes. The high-speed backbone is typically connected in a point-to-point relay fashion with other field boxes and then to a central recording system where all of the data are recorded onto a mass data storage medium, such as a magnetic tape.
In another seismic data acquisition system configuration, the data is recorded at the field boxes coupled to the sensors and such field boxes communicate with the central control unit over a radio frequency. The data from such field boxes is typically collected by a transcriber in the field and transferred to the central control unit.
To perform a seismic survey, a survey plan is made that includes the location of each sensor in the array and the location of each source shot. The actual location of the shots may differ because it is not feasible to activate a source at the planned location or that even after locating a stake at such location, such stakes are moved, knocked down, and/or blown over, and/or removed and/or destroyed completely. Even if the stake marker is accurate, the actual seismic source may be positioned inaccurately. Navigation tools, such as geo-positioning tools, are used to record the actual sensor and source shot locations. The source parameters are maintained at a data collection point or at a central controller and entered into the trace data after collecting such from the various data acquisition units. The pre-processing task of entering the source, receiver and other parameters, such as spatial coordinates, etc. for each trace data can be arduous, time-consuming, and prone to errors.
Thus, there is a need for an improved method and system for associating the source parameters with the sensor data during seismic data acquisition.